Particle counter and classification system

ABSTRACT

A particle counter and classification system including an imaging subsystem configured to determine the size and morphology of particles above a predetermined size in a fluid in a sample cell. A first stage magnetometer sensor subsystem is tuned to detect and determine the size of ferrous and/or conducting particles. An optional second stage magnetometer sensor subsystem is tuned to detect the overall ferrous particle content of the fluid. A processor subsystem is configured to calculate and report the number of particles in the fluid in a plurality of size ranges, their morphology, their classification as a particular particle type according to their characteristic morphology, the number of ferrous and/or conducting particles, and the overall ferrous content of the fluid.

FIELD OF THE INVENTION

This invention relates to particle counters, magnetometers, and theclassification of particulate in a fluid via particle imaging.

BACKGROUND OF THE INVENTION

The number of particles in a fluid sample, their size, and shape(morphology) can be determined by an imaging apparatus as shown, forexample, in U.S. Pat. Nos. 5,572,320; 7,385,694; 5,627,905; 5,959,668;6,049,381; 6,104,483; 6,501,504; 6,873,411; 7,019,834; 7,184,141;7,307,717; 7,385,694; 7,921,739; 8,056,400 and 8,079,250 allincorporated herein by this reference. There is typically, however, nodifferentiation made between magnetic and non-magnetic particles. Thisinformation is important to maintenance personnel.

Magnetometers can be used to determine the overall percent offerromagnetic particles in oil, or to provide information regarding thesize and magnetic nature (ferromagnetic or non-ferromagnetic) ofindividual particles greater than a certain minimum size threshold. See,for example, U.S. Pat. Nos. 5,001,424; 5,315,243; 5,444,367; 5,404,100;5,811,664 and 6,051,970 all incorporated herein by this reference. Suchdevices, however, do not classify the magnetic particles according tomorphology. In addition, such devices typically either supply an overallferromagnetic percent or information regarding individually observedparticulate, but not both.

SUMMARY OF THE INVENTION

A particle counter and classification system with an imaging apparatusand a magnetometer type device enables, for example, the user todetermine which particles of a given shape or size is either (1)ferromagnetic, (2) non-ferromagnetic and electrically conducting or (3)non-ferromagnetic and non-conducting.

In one example, a particle counter and classification system providesfor the determination of the size and shape of magnetic and conductingparticles, quantifies magnetic and conducting particles, and in oneexample, separately analyzes non-metallic particles.

In one preferred embodiment, a dual-stage magnetometer is positionedbehind an analysis cell associated with a particle imaging apparatus. Inthis way, particles from the same fluid can be imaged and counted. Thesesame particles can then be characterized for their individual magneticand conducting content using the dual-stage magnetometer. Finally, thedual-stage magnetometer can report the overall magnetic content of thefluid, which allows for particles which are too small to be imaged orcharacterized individually to be accounted for.

Featured is a particle counter and classification system comprising animaging subsystem configured to determine the size and morphology ofparticles above a predetermined size in a fluid in a sample cell. Afirst stage magnetometer sensor subsystem for the fluid is tuned todetect and determine the size of ferrous and/or conducting particles inthe fluid above the predetermined size. A second stage magnetometersensor subsystem for the fluid is tuned to detect the overall ferrousparticle content of the fluid. A processor subsystem is responsive tothe imaging subsystem, the first stage magnetometer sensor subsystem,and the second stage magnetometer sensor subsystem. The processorsubsystem is configured to calculate and report the number of particlesin the fluid in a plurality of size ranges, their morphology, theirclassification as a particular particle type according to theircharacteristic morphology, the number of ferrous and/or conductingparticles in said size ranges, and the overall ferrous content of thefluid.

The imaging subsystem may include a light source directingelectromagnetic radiation into the sample cell and a detector responsiveto electromagnetic radiation emitted from the sample cell. The firststage magnetometer sensor subsystem may include a small diameter fluidconduit upstream or downstream of the sample cell with a small diametersense coil thereabout and the second stage magnetometer sensor subsystemmay include a larger diameter fluid conduit downstream of the samplecell with a larger diameter sense coil thereabout. The larger diameterfluid conduit may be downstream of a small diameter fluid conduit. Thefilling factor of the small diameter sense coil is preferably optimizedfor ferrous and/or conducting particles imageable by the imagingsubsystem. The filling factor of the large diameter sense coil ispreferably optimized for ferrous particle sizes below and above saidpredetermined size. The first stage magnetometer sensor subsystem mayfurther include an impedance monitor configured to detect the amplitudeand phase of the voltage of the small diameter sense coil. The secondstage magnetometer sensor subsystem may further include an impedancemonitor configured to detect the amplitude and phase of the voltage ofthe larger diameter sense coil. In one design, the small diameterconduit is between 250 and 750 microns in diameter and the largerdiameter conduit is between 1,500 and 15,000 microns in diameter.

Also featured is a particle counting and classification method.Particles in a fluid are imaged to determine their size and, forparticles above a predetermined size, to determine their morphology.Ferrous and/or conducting particles above the predetermined size aredetected and, for the ferrous and/or conducting particles above thepredetermined size, the number of the ferrous and/or conductingparticles in a plurality of size ranges is counted. The method furtherincludes detecting ferrous particles above and below a predeterminedsize and calculating the overall ferrous particle content of said fluid.Detecting ferrous and/or conducting particles above said predeterminedsize may include passing the fluid through a first stage magnetometersensor subsystem with a small diameter fluid conduit having a smalldiameter sense coil thereabout and detecting ferrous and/or conductingparticles above and below the predetermined size includes passing thefluid through a second stage magnetometer sensor subsystem with a largerdiameter fluid conduit having a larger diameter sense coil thereabout.Detecting ferrous and/or conducting particles above said predeterminedsize may include detecting the amplitude and phase of the voltage of thesmall diameter sense coil. Detecting ferrous particles above and belowthe predetermined size may include detecting the amplitude and phase ofthe voltage of the larger diameter sense coil.

Also featured is a particle counter and classification system comprisingan imaging subsystem configured to determine the size and morphology ofparticles above a predetermined size in a fluid in a sample cell, afirst stage magnetometer sensor subsystem for the fluid tuned to detectand determine the size of ferrous and/or conducting particles in saidfluid above said predetermined size, and a processor subsystem,responsive to the imaging subsystem and the first stage magnetometersensor subsystem, configured to calculate and report the number ofparticles in the fluid in a plurality of size ranges, their morphology,their classification as a particular particle type according to theircharacteristic morphology and the number of ferrous and/or conductingparticles in said size ranges.

The system may further include a second stage magnetometer sensorsubsystem for said fluid tuned to detect the overall ferrous particlecontent of the fluid. The processor subsystem is configured to initiallyclassify said particles in different size ranges based on the output ofsaid imaging subsystem and to adjust said initial classification basedon the output of said first stage magnetometer sensor subsystem.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features, and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a block diagram showing the primary components associated withan example of a particle counter and classification system in accordancewith the invention;

FIG. 2 is a schematic cross sectional view showing portions of the firstand second stage magnetometer sensor subsystems associated with thesystem shown in FIG. 1;

FIG. 3 is a schematic view showing a report displayed on the displayshown in FIG. 1 generated by the processor subsystem of FIG. 1;

FIG. 4 is a schematic diagram of an example of the drive circuitry andimpedance monitoring circuitry for the system of FIG. 1; and

FIG. 5 is a flow chart depicting the primary steps associated withprogramming of the processor subsystem depicted in FIG. 1.

FIG. 6 is a mechanical drawing of one embodiment of the overall system.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

FIG. 1 depicts an example of a particle counter and classificationsystem 10 including imaging subsystem 12 with flow cell 14 through whicha fluid (e.g., oil) sample passes. The sample may be fluid diverted viaa bypass conduit in a machine (e.g., engine or motor) or may be a sampleobtained from a machine and delivered to an analyzer. Laser 16 directselectromagnetic radiation into sample cell 14 and detector 18(including, for example, a CCD) images the contents of the cell as isknown in the art.

Electronic signals output by detector 18 concerning the number, size,and shape of particles in the fluid is processed by processor subsystem20 responsive to detector 18. Processor subsystem 20 may be a computer,a microprocessor based electronic subsystem, a field programmable gatearray appropriately programmed, an application specific integratedcircuit or the like. The processor subsystem may be distributed amongstvarious devices and/or circuitry in some examples.

Imaging subsystem 12 is configured (using optical devices if necessary)to focus appropriately on certain size particles of interest, typicallybetween 20 and 100 microns. Imaging subsystem 12, for certain particlesize ranges, can detect the particles, determine their size, determinetheir morphology (shape) and processor subsystem 20 can includealgorithms to categorize the particles (for example, particles generatedby cutting wear, particles generated by sliding wear, and the like). Thedepth of field necessary to sharply image particles of interest can beconfigured and/or adjusted as necessary. The imaging subsystem, however,can also detect and determine the size of smaller particles such asparticles between 4 microns and 20 microns. For those particles,however, the imaging subsystem cannot typically determine their shapenor can they be categorized.

After passing through cell 14 the fluid proceeds or is delivered tofirst stage magnetometer sensor subsystem 22 a tuned to detect anddetermine the size of ferrous and/or conducting particles in the fluidimaged by the imaging subsystem 12. Note that the fluid may also bedelivered first to magnetic sensor subsystem 22 a and then to cell 14.In this particular example, first stage magnetometer sensor subsystem 22a includes first stage magnetometer head 24 a, FIG. 2 typically aplastic fluid conduit with driving and sensing coils thereabout. FIG. 2depicts only one sense coil 42 a for clarity. Drive circuitry 26 a, FIG.1 energizes the drive coil(s) and impedance monitor 28 a reports theamplitude and phase change of the voltage sense coil(s) representing thepresence of ferrous and/or conducting particles passing through thesmall diameter (e.g., 500 micron) conduit 40 a. This first stagemagnetometer sensor subsystem 22 a, FIG. 1 may include copper drivewindings over copper sense windings. A dummy coil arrangement may beincluded about a conduit with no fluid flowing through it also having anoutput directed to processor subsystem 20.

Impedance monitor 28 a provides an output signal to processor subsystem20 configured or programmed to report via display 30 the number offerrous particles in various size ranges optionally using data obtainedfrom imaging subsystem 12 typically upstream of first stage magnetometersensor subsystem 24 a. The result is a report including the number ofparticles in each size range (and optionally their shape or othermorphology information) and how many of those particles in that sizerange are ferrous or conducting as shown in FIG. 3.

The second stage magnetometer sensor subsystem 22 b, FIG. 1 ispreferably located downstream of first stage magnetometer sensorsubsystem 22 a and includes, as shown in FIG. 2, a much larger (e.g.,15,000 micron) size fluid plastic conduit 40 b with driven and sensingcoils thereabout such as sense coil 42 b. The drive coil(s) areenergized by drive circuitry 26 b, FIG. 1 and impedance monitor 28 breports the amplitude and phase change of the voltage sense coil(s) toprocessor subsystem 20. Again, a dummy coil arrangement may be used forsecond stage magnetometer sensor subsystem 24 b. Second stagemagnetometer sensor subsystem 22 b is tuned to detect the overallferrous particle content of the fluid and processor subsystem 20 reportsthis data to display 30 as shown in FIG. 3.

The first stage 22 a is specifically designed to be sensitive toparticulate for which morphology information can be obtained by theimaging subsystem. The miniature bore magnetometer head is designed sothat the filling factor of the sense coil is optimized for particles ina particular equivalent circular diameter range. In one embodiment, thisapparatus would be sensitive to particles with equivalent circulardiameter of 20 microns and greater. The magnetometer electronics aredesigned to report the amplitude and phase of the voltage of the sensecoil associated with each particle.

The second stage of the magnetometer, in contrast, is designed such thata separate and distinct set of coils, typically with much larger radius,provide an optimal reading of the overall magnetic content of a fluid.Assuming the distribution of particulate of all sizes within the fluidis homogeneous, the overall magnetic content of the fluid increases in apower-law fashion as the radius of the sense coil and fluid flowingthrough the coil increases. At the same time, the field strength perunit volume of a solenoid need not decrease in such a cubic fashion asthe radius of the sense coil increases. Thus, there are many optimalsensitivity designs which include larger radii sense coils which may bechosen to report the overall magnetic content of the fluid. Note that,in general, such coils will not be appropriate for individualparticulate since their fill factor for individual particulate will ingeneral be much less. Such a magnetometer can operate separately fromthe imaging subsystem as well, in cases where no imaging apparatus isrequired.

In one embodiment, the dual-stage magnetometer includes, for Stage 1, a2-layer excite/sense solenoid design connected in a bridge arrangementwith an identical excite/sense solenoid. Such a 4-coil system is thenexcited with a drive voltage which is fed into a synchronousdemodulation circuit. Once zeroed, such a circuit produces the amplitudeand phase of the signal due to individual particles passing through theactive solenoid. Through filtering the resulting signal through a bandpass circuit based on the expected oscillation profile due to individualparticulate, a highly sensitive individual particulate monitoringmagnetometer stage is realized. For Stage 2, an identical magneticdesign using a much larger solenoid radius is chosen. An identicalexcitation/demodulation circuit is also chosen but in this case, the(unfiltered) dc signal, which provides the amplitude and phase of theoverall magnetic content of the fluid, is probed. Stage 1 and Stage 2are coupled via flow tubing which is appropriately sized for each stage.

In this way, a unique dual-stage magnetometer arrangement is achieved.Such a dual-stage magnetometer can have substantial benefit relative toconventional magnetometers, including but not limited to, the fact thatthe signals arising from both stages may be compared to each other toprovide further validation and robustness to the particle and overallmagnetic content algorithms employed by processor subsystem 20 todetermine such quantities.

Using statistical techniques, processor subsystem 20, FIG. 1 presentedwith signals from imaging subsystem 12, first stage magnetometer sensorsubsystem 22 a, and optionally second stage magnetometer sensorsubsystem 22 b and is programmed to calculate and report the number ofparticles in the fluid in a plurality of size ranges, their shape, thenumber of ferrous particles in those size ranges, and the over allferrous content of the fluid. Moreover, the calculations of the ferrouscontent based on data from first stage magnetometer sensor subsystem 22a and/or second stage magnetometer sensor subsystem 22 b can depend onor be based on the data from imaging subsystem 12.

For example, the imaging subsystem 12 may provide an initialclassification by identifying all wear debris, which can be eitherconducting (e.g., Copper) type and/or ferromagnetic (e.g., Iron) type.Based on this classification, the first stage magnetometer subsystem 22a, may then provide a positive identification as to the type of theidentified wear debris. The wear debris count and size statistics maythen be updated. If as a result of imaging subsystem 12 there were 62identified wear particles in the 25 micron size bin, and the first stagemagnetometer subsystem identifies 55 ferromagnetic particles in the 25micron size bin, the processor subsystem 20 may report that 88.7% ofidentified wear debris in the 25 micron size bin was ferrous. Further,if the results show that as a result of subsystem 22 a that 128 wearparticles are identified as being ferromagnetic, this may indicate thatthe original wear debris classification of all particulate identifiedmay need to be refined to classify more particles as being wear debris.This may trigger a reclassification of all particulate using modifiedclassification criteria so that the total amount of wear debris in the25 micron size bin has at least 128 particles. In this way, the firstmagnetometer subsystem 22 a may provide feedback to improve the qualityof the classifier operating on imaging subsystem 12. Such calculationsconcerning the particulate would not be possible without combining thedata from subsystems 12 and 22 a analyzing the same aliquot of fluid.The processor subsystem 20 may classify individual particulateidentified by imaging subsystem 12 as being either cutting, sliding orfatigue wear particles, non-metallic particles, fibers, water droplets,or air bubbles. The processor subsystem 20 may then in turn utilize thisinformation in conjunction with the information provided by the firststage magnetometer subsystem 22 a to provide targeted ferrous andconducting particle count information on the specific cutting, sliding,and fatigue wear particles identified using the processor subsystem'sanalysis of imaging subsystem 12 information. In this example, theprocessor subsystem 20 may provide magnetic particle count informationas a percentage of the total number of cutting, sliding, and fatiguewear particles identified in all size bins (20, 21, 25, 38, 50, 70, 100microns).

As shown in FIG. 3, the imaging subsystem 12, FIG. 1 is able to detectand count particles between 4 to 100 microns in this example but canonly image, size, and classify particles between 20 and 100 microns. Forexample, in this particular scenario shown, there were five particles 21microns (or greater) and based on their shape, processing subsystem 20has classified four of these particles from cutting type wear and one ofthese particles resulting from sliding type wear as shown in FIG. 3.

First stage magnetometer sensor subsystem 22 a, FIG. 1 is tuned to countand size ferrous particles between 20 microns and 100 microns in severalsize ranges. Note the this information combined with the informationprovided by the imaging subsystem enables the analyst to readily seethat four out of five particles in the size range of 21 microns (orgreater) were due to cutting wear and were magnetic. This could indicateto the analyst, for example, that a machine's steel alloy bearings arewearing as opposed to cutting wear shaped particles from an aluminum orother non-ferrous part or subsystem such as an oil pump mostly includingnon-magnetic components.

Second stage magnetometer sensor subsystem 22 b, FIG. 1 is tuned todetect the overall magnetic content and typically provides no sizeinformation. Instead, second stage magnetometer sensor subsystem 22 bdetects particles as small as four microns and as large as 100 micronsand, importantly, provides information concerning small size ferrousparticles (e.g., 0 to microns) that imaging subsystem 12 and first stagemagnetometer sensor subsystem 22 a cannot.

Processor subsystem 20 is configured to analyze the signals output bythe imaging subsystem 12, first stage magnetometer sensor subsystem 22a, and second stage magnetometer sensor subsystem sensing sensorsubsystem 22 b as follows.

If a small sized particle (e.g., four microns) is present in a fluidsample, imaging subsystem 12 can detect the particle and determine itssize but cannot obtain a sufficient image of the particle in order todetermine the shape of such a small particle and/or its category, forexample, whether the particle was generated by sliding wear or cuttingwear. The output signal of imaging subsystem 12 thus presented toprocessor subsystem 20 enables processor subsystem 20 to report only thesize of this particle and to add it to the count of particles sized fourmicrons (and greater).

First stage magnetometer sensor subsystem 22 a typically provides norelevant data concerning such a small sized particle because it is tunedto particles in the size range (e.g., 20 microns to 100 microns) whichare fully imageable by the imaging subsystem. Second stage magnetometersensor subsystem 22 b, however, detects this four micron particle if itis a ferrous particle. Knowing the volume of fluid, the processorsubsystem 20, responsive to a signal from impedance monitor 28 b, addsthis particle to the concentration (e.g., parts per million) calculationfor ferrous particles in the overall magnetic content report.

When a larger particle (e.g., 25 microns) is present in the fluidsample, imaging subsystem 12 detects this particle and provides a signalregarding its size and shape. Processor subsystem 20 then categorizesthis particle based on its shape (e.g., sliding wear, cutting, or thelike) and reports the result. Processor subsystem 20 also adds thisparticle to the count of those size particles in the sample. First stagemagnetometer sensor subsystem 22 a detects whether this particle isferrous and/or conducting and if so outputs a signal which enablesprocessor subsystem 20 to size the particle and add it to the count offerrous and/or conducting particles of that size. If this particle isferrous, second stage magnetometer sensor subsystem 22 b also reportsthis particle to processor subsystem 20 which adds it to the overallmagnetic content parts per million calculations. Thus, for particlesgreater than 20 microns in size, the output of first stage magnetometersensor subsystem 22 a and second stage magnetometer sensor subsystem 22b provide some redundant information which can either be ignored or usedin algorithms to refine the output provided by processor subsystem 20 asit uses the redundant information to make corrections to the finalreport.

The following chart summarizes the capabilities of each subsystem:

Size Identify Determine Determine (microns) Detect as ferrous size shapeClassify  4-20 Imager 2^(nd) stage 2^(nd) stage (if ferrous) 20-100Imager 1^(st) stage Imager Imager Imager 1^(st) stage 2^(nd) stage1^(st) stage (if ferrous) (if ferrous) 2^(nd) stage (if ferrous)

Thus, for particles 20-100 microns in size, the imager combined with thefirst stage magnetometer sensor subsystem provides key informationconcerning the same fluid sample. Here, the second stage magnetometersensor subsystem supplements the first stage for redundancy androbustness.

For particles smaller than 20 microns, e.g., 4-20 microns, the imagerdetects them and keeps count of particles in various size bins and thesecond stage magnetometer subsystem enables a more accurate count of theoverall magnetic particle concentration in these size ranges where thefirst stage magnetometer subsystem cannot.

FIG. 4 illustrates the electronics of the subject invention. TheQuadrature Square Wave Generator 50 generates a two-bit binary graycode. The sequence is 00, 01, 11, 10. Each state persists for about 11.4microseconds, and the complete sequence repeats every 45 microseconds.The result is two pulse trains (TTLSON and TTLCOS), each having afrequency of 22 kHz and a duty cycle of 50%, and are thus square waves.There is an 11 microsecond delay between the two signals, equivalent toa phase shift of 90 degrees. The outputs have normal CMOS output levels.

The Amplitude Regulator 52 takes the square wave output from theQuadrature Square Wave Generator and produces a waveform having the sametiming but having well-defined high and low voltage levels. This is doneby creating two DC voltages, approximately 2.5 and 7.5V, in which thevoltage difference between these two voltages is precisely controlled tobe 5V. An analog switch alternates between these two voltages, producinga square wave with precisely controlled amplitude of 5V p-p.

The Low Pass Filter 54 is a three-pole Sallen-Key filter with a gain of1.5 and a −3 db point of about 15 kHz. This filter attenuates theharmonics of the input square wave, making the waveform close to a sinewave.

The Driver Amplifiers 54 use high-power operational amplifiers in aninverting configuration. Their gain is 1.47, but this can be tailoredfor different applications. In their standard configuration, the outputvoltage is about 10V p-p.

The Balance Adjust network 57 consists of two potentiometers that areused to adjust the output of the coils so that the output is near zerowhen no sample is introduced into the cell. Each potentiometer isconnected between the coil drive signal and ground. Thus the wiper ofeach potentiometer produces a voltage that is an adjustable fraction ofthe drive voltage. One potentiometer has a resistor connected from thewiper to the junction of the two drive coils. The second potentiometerhas a capacitor connected from the wiper to the junction of the twodrive coils. When the potentiometers are set with the wipers athalf-scale, no current will flow through the resistor or the capacitorbecause both ends of the resistor or capacitor are at half of the drivevoltage, and so the voltage across the resistor or capacitor is zero. Ifone of the potentiometers is adjusted away from this position, currentwill flow through the resistor or capacitor. Since the ac currentthrough a capacitor is 90 degrees ahead of the current through aresistor, any phase or magnitude of adjustment is possible.

The Balance Coil is described elsewhere. In short it consists of twotransformers with the primaries connected in series and the secondariesconnected in anti-series. It is excited by the 10V p-p drive voltage andits output is nominally zero under balanced conditions (no sample incell).

The sense amplifier 58 is a three-stage high gain amplifier having again of about 2000 and a band-pass characteristic. The first stage is alow-noise amplifier suited to amplifying the low-impedance output of thesense coils. Its gain is 100 and it has a low-pass characteristic. Thesecond stage is a gain of ten bandpass, and the third stage is a gain oftwo bandpass.

Each channel has two demodulators 60, 62, one for the imaginarycomponent and one for the real component. The two demodulators are usedtogether to determine the size of a particle and to determine whetherthe particle is ferrous or conductive. Each demodulator consists of aninverting amplifier with a gain of −1, followed by an analogmultiplexer. Each multiplexer alternately connects its output to eitherthe input or the output of the inverting amplifier. The multiplexer'scontrol input is driven by the output of the Quadrature Square WaveGenerator. The output of the demodulator is thus sensitive to inputs atthe frequency of the drive voltage, and rejects other frequencycomponents in the signal. It is also phase sensitive, rejecting signalsthat are phase shifted by 90 degrees from the control signal.

The Low Pass Filter 64 is a MFB (Multiple Feedback) low-pass filterhaving a gain of 2 and a −3 db point of about 100 Hz. It smooths theoutput of the demodulator to produce a ripple-free waveform.

The ADC 66 converts the output of the filter to digital ‘bin’. It is a16-bit SAR (Serial Approximation Register) converter. The MicroController 68 takes the digital values from the four ADC's, formatsthem, and transmits them through a serial port.

It can be seen that the electronics provide for a two-channel instrument(magnetometer subsystems 22 a and 22 b each representing one channel)that uses the magnetic properties of a material in a carrier such asoil, to determine the material's size, concentration and composition. Itoperates by sensing the change in inductance of a coil when a smallamount of ferrous or conducting material is introduced into a samplecell inside the coil.

It is desirable to detect the smallest possible quantity of material,and so it is necessary to detect a small change in inductance. Thecurrent embodiment can detect a change of about 1 part in 10⁷ ininductance.

For each channel, a dummy coil, having nominally the samecharacteristics as the sensing coil but not magnetically coupled to it,is put in series with the sensing coil, and an AC excitation voltage isapplied to the series pair. Thus without any ferrous or conductingmaterial, the voltage at the junction of the two coils would be half ofthe excitation voltage. Changes in the characteristics of the coils dueto environmental conditions (such as temperature) would normally maskthe small measurement, but with matched coils the output would remain athalf of the excitation.

Though the dummy coil stabilizes the signal to be measured, it is stillnecessary to measure a very small voltage change (microvolts) on a largevoltage (volts). This would require a measurement system stable tosub-ppm levels, which is not practical. To alleviate this requirement,each coil is provided with a secondary winding which is wound on top ofthe primary winding, with close magnetic coupling. Thus the secondarywinding will generate a voltage which is closely proportional to theback EMF of the primary winding. Because these secondary coils are notelectrically connected to the primary coils, the secondary of thesensing coil may be wired in anti-series with the secondary of the dummycoil. The net output of this pair is the difference between the backEMF's of the two coils.

Because of the matching of the two coils, this output voltage would bezero if no ferrous or conducting material is present. In practice thetwo coils would not be perfectly matched, and so the output woulddeviate from zero in proportion to the matching. There are alsoparasitic capacitances in the coils that unbalance the coil pair. Inpractice the output should be matched to within a small fraction of 1%.Even this small imbalance is many times larger than the signals to bemeasured. This imbalance is corrected in the electronics.

A ferrous particle changes the inductance of the coil, while aconducting particle changes the resistance of the coil. Thus the changein output voltage of the coil is 90° out of phase for the two types ofparticles. With appropriate signal processing, the phase of the voltagechange can be measured and the two types of particles can bedistinguished. The block diagram in FIG. 4 shows the major functionalsections of the electronics. The description refers to the circuitryassociated with coil pair #1 (associated with magnetometer subsystem 22a) unless noted.

The coils are excited with a 22 kHz pseudo-sine wave. A QuadratureSquare Wave Generator 50 creates two digital square waves, TTLSIN andTTLCOS. In Amplitude Regulator 52, TTLSIN is used to generate anothersquare wave having extremely stable amplitude characteristics. Thissquare wave is passed through the Low Pass Filter 54 which attenuatesthe harmonics of the square wave. Since the harmonics are not completelyremoved, the waveform is not exactly sinusoidal, thus the labelpseudo-sine. This signal is fed to Driver Amplifier 54 which changes thevoltage and provides high current drive capability to drive the coilpair. Coil pair #2 (associated with magnetometer subsystem 22 b) has itsown amplifier 56 which may have a different gain to provide a differentdrive voltage to coil pair #2.

The Drive Amplifier connects to the series pair of coils. As notedabove, the coil pair may be imbalanced and generate a non-zero outputwith the sample cell empty. The Balance Adjust circuit cancels thisimbalance by injecting a small adjustable AC current into the junctionbetween the two coils. The imbalance may have any phase, so twoindependently adjustable currents are injected. One is injected througha resistor, while the other is injected through a capacitor. Thecurrents are 90° out of phase with each other, so by varying theiramplitudes any imbalance may be cancelled.

As described above, the coil primaries are in series and the secondariesare in anti-series. This in combination with the imbalance adjustmentprovides an output signal that is typically in the range of 0-1millivolt peak-to-peak. The Sense Amplifier 58 has a gain in the lowthousands, and in addition provides several stages of high- and low-passfiltering.

The output of the Sense Amplifier is demodulated at 60 using andinverting amplifier and an analog switch. The inverting amplifier has again of −1, producing a 180° phase-shifted version of the senseamplifier output. The analog switch is driven by the TTLSIN signal,which is a square wave at the same frequency as the amplifier output.When TTLSIN is high, the amplifier output is selected, while when TTLSINis low, the inverted output is selected. Thus an AC signal from theamplifier, having no DC component, is converted to a pulsating DC levelthat is proportional to the AC amplitude.

A second demodulator 62 is used to detect signals that are not in phasewith TTLSIN and would not produce an output from the first demodulator.It works the same way as the first demodulator but is driven by TTLCOS,which is 90° out of phase with TTLSIN. The output of the twodemodulators provides a real and imaginary component of a complex numberthat describes the magnitude and phase of the Sense Amplifier output.

Low Pass Filter 64 is used to eliminate the pulsations in the outputs ofthe Demodulators. It is a two-pole filter with a 100 Hz knee and a DCgain of 2.

ADC 66 converts the output of the Low Pass Filter. It is a 16-bit, 8channel SAR type ADC with an internal 2.5V reference and a signal rangeof 0-2.5V. The ADC converts all four Filter outputs at a rate of 500samples/second for each channel (total sample rate of 2000samples/second). Since it is a single ADC with a multiplexer, theacquisition is not simultaneous. The skew is made as small as isconvenient based on programming considerations, simply by taking each ofthe four samples in succession.

The microcontroller receives the ADC samples and formats the four 16-bitvalues into a comma separated ASCII stream terminated with <cr><lf>. Thestream is sent out of a USB port with no handshaking. This USB porttransmits the data from magnetometer subsystems 22 a and 22 b to theprocessor subsystem 20, FIG. 1. Transmission begins upon powerup of themicrocontroller.

FIG. 5 shows the primary steps associated with the programming ofprocessor subsystem 20, FIG. 1. The image processor utilizes, in oneexample, a k-nearest neighbor (k-NN) classification technique which isbuilt from a library of known particle types, in classifying eachparticle as being wear (cutting, sliding, fatigue), non-metallic,fibrous, water or air. The image processor then classifies individualparticles into size bins of equivalent circular diameter. It achievesthis by calculating the measured area of the particle from the imageitself and then calculating diameter of a circle with an equivalentarea. The result is that each particle is tagged with both an equivalentdiameter and type classification. Input from the first-stagemagnetometer may serve as feedback to the k-NN to increase the number ofnearest neighbors classified by 1, for example. The imaged particles canthen be reclassified to determine if such an adjustment increased thenumber of particles classified as wear debris. This process can berepeated until the numbers provided by the imager and first-stagemagnetometer at least coincide.

FIG. 5 describes the primary steps which are taken on the data acquiredby each of the three subsystems which acquire information on theparticle-laden fluid. For the imaging subsystem 20, an image map of eachindividual particle greater than 20 microns which are detected by thesubsystem is generated. Such a map constitutes a sequential listing ofall the particle images. With this in hand, the next step is to use theclassification scheme of the system, which references a particle typelibrary, in order to classify each particle in the map is being eitherwear-generated, non-metallic, fibrous, water or air. Depending on theneeds of the system other such classification families may also begenerated. The result of this analysis, and the determination of thesize of the particle through calculating an equivalent circular diameterof the image, is then fed into the overall summary display.

For first stage magnetometer subsystem 22 a, a listing of the particleevents detected is generated. A particle event is typicallycharacterized by a short-duration (˜0.1 seconds) increase in the outputvoltage of the subsystem 22 a. Such events are determined by athresholding algorithm which examines events a number of standarddeviations above the quiescent output of the subsystem 22 a, andcertifies them as actual events if their characteristic voltage vs. timesignature is sufficiently different from a typical noise signature(determined dynamically on the output). These events are classifiedaccording to the electromagnetic nature of the event, i.e., it isdetermined if the event is from a primarily ferromagnetic particle orfrom a highly conducting particle. This is accomplished by examining the2-channel output of the electronics and simply noting if the signaloccurred on the imaginary channel (and hence is ferromagnetic) or thereal channel (and so conducting). From this listing of events, theequivalent circular diameter of each particle is determined by a fixed,stored calibration of the net peak output voltage to equivalent circulardiameter of the particle. The result is a listing of particle events,the size and electromagnetic nature of each event, which can then be fedinto the overall summary display.

For the second stage magnetometer subsystem 22 b, the overall part permillion (ppm) weight of the fluid is determined. This is accomplished byrecording the average output voltage (over a period of approximately 10seconds) of the magnetometer 22 b on the imaginary (ferromagnetic)output channel when fluid is injected into the flow line which travelsthrough the coil. Next, the fluid is flushed out of the flow line and isreplaced with cleaning fluid of a known type (such as Electron 22solvent). The output voltage of 22 b on the imaginary output channel isagain recorded and averaged over a period of approximately 10 seconds.From the difference of these two voltages, a stored linear calibrationto the overall ppm weight of the fluid to this resultant voltageprovides the ppm outputted to the overall summary display.

The overall summary display is then utilized to provide information fromall three measurement subsystems 20, 22 a, and 22 b, in a way that fusesthis content to provide the most comprehensive information possible tothe user. An example display is shown in FIG. 3. For each size bin, thefollowing information is provided: (1) the total number of particleswhose equivalent circular diameter is greater than or equal the size ofthat bin, (2) (if larger than 20 microns) the image classificationsummary statistics of (1), (3) the number (or percentage or both) offerromagnetic and conducting particles in that same size bin. Alsorepresented is the total ferrous content (in ppm) of the fluid. Theimages of the individual particles may also be present for viewing. Atypical machinery wear situation illustrates the utility of fusing theinformation in this fashion: A significant amount of wear debrisgenerated by the engine on large machinery, along with a small amount ofdirt, may be present in the oil of a new engine upon startup. This wouldtypically be reflected in elevated total particle counts in the smallsize bins, as well as elevated numbers of particles classified as weardebris and non-metallic. The wear debris particles identified at startupwill be a mixture of ferromagnetic and conducting, so the total numberof wear particles should be a split between ferromagnetic and conductingparticles. The overall ferrous ppm reading may be slightly elevated at areading of 20 ppm. As the engine heads towards a breakdown, anincreasing total number of particles may be noted, along with anincreasing number of particles in the larger size bins, as a percentage,relative to the numbers in the smaller diameter particle bins. Theoverall ferrous ppm reading will be continually elevated and may reachlevels of 100 ppm. The larger particles are a sign that the engineitself is creating a large number of sliding and cutting wear debrisparticles. This contrasts with the profile that may be seen from anengine that has seen a significant amount of service but is notbeginning a breakdown mode. Often, the engine oil will accumulate asignificant amount of dirt due to its heavy usage and the aging ofseals. In this case, all of the overall particle count levels may besimilar, as well as the overall ferrous ppm reading (100 ppm). However,we will see a clear indication in the ferromagnetic particle count,which may be 20% of the total number of particles in given bin, eventhough there are significantly elevated overall counts in that same bin,including particles classified as wear debris.

FIG. 6 shows the fluid portion through the magnetometers and the flowcell imager. Fluid from a sample bottle 69 may be urged by a pump 70through first-stage magnetometer 22 a, flow cell 14, and second-stagemagnetometer 22 b. A valve 71 may be activated by pressure sensors 72,73 when needed, typically to bypass the high flow restriction flow cell14 for optimal cleaning.

Thus, although specific features of the invention are shown in somedrawings and not in others, this is for convenience only as each featuremay be combined with any or all of the other features in accordance withthe invention. The words “including”, “comprising”, “having”, and “with”as used herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

What is claimed is:
 1. A particle counter and classification systemcomprising: a detector subsystem configured to detect and determine thesize of particles above a predetermined size in a fluid in a samplecell; a first stage magnetometer sensor subsystem for the fluid tuned todetect and determine the size of ferrous and/or conducting particles insaid fluid above said predetermined size; a second stage magnetometersensor subsystem for said fluid tuned to detect the overall ferrousparticle content of the fluid; and a processor subsystem, responsive tothe detector subsystem, the first stage magnetometer sensor subsystem,and the second stage magnetometer sensor subsystem, configured tocalculate and report the number of particles in the fluid in a pluralityof size ranges, the number of ferrous and/or conducting particles insaid size ranges, and the overall ferrous content of the fluid, andfurther configured to classify individual particles detected by saiddetector subsystem and to reclassify said individual particles based onfeedback information from said first stage magnetometer sensorsubsystem.
 2. The system of claim 1 in which the detector is a componentof an imaging subsystem including a light source directingelectromagnetic radiation into the sample cell and the detector isresponsive to electromagnetic radiation emitted from the sample cell. 3.The system of claim 1 in which the first stage magnetometer sensorsubsystem includes a small diameter fluid conduit upstream or downstreamof the sample cell with a small diameter sense coil thereabout and thesecond stage magnetometer sensor subsystem includes a larger diameterfluid conduit downstream of the sample cell with a larger diameter sensecoil thereabout.
 4. The system of claim 3 in which the larger diameterfluid conduit is downstream of the small diameter fluid conduit.
 5. Thesystem of claim 3 in which the filling factor of the small diametersense coil is optimized for ferrous and/or conducting particles imagableby the imaging subsystem.
 6. The system of claim 3 in which the fillingfactor of the large diameter sense coil is optimized for ferrousparticle sizes below and above said predetermined size.
 7. The systemclaim 3 in which the first stage magnetometer sensor subsystem furtherincludes an impedance monitor configured to detect the amplitude andphase of the voltage of the small diameter sense coil.
 8. The system ofclaim 3 in which the second stage magnetometer sensor subsystem furtherincludes an impedance monitor configured to detect the amplitude andphase of the voltage of the larger diameter sense coil.
 9. The system ofclaim 3 in which the small diameter conduit is between 250 and 750microns in diameter.
 10. The system of claim 3 in which the largerdiameter conduit is between 1,500 and 15,000 microns in diameter.
 11. Aparticle counting and classification method comprising: detectingparticles in a fluid to determine their size; detecting ferrous and/orconducting particles above a predetermined size and, for said ferrousand/or conducting particles above said predetermined size, counting thenumber of said ferrous and/or conducting particles in a plurality ofsize ranges; detecting ferrous particles above and below saidpredetermined size and calculating the overall ferrous particle contentof said fluid; classifying individual particles; and reclassifying saidindividual particles based on identification of said individualparticles as ferrous and/or conducting particles.
 12. The method ofclaim 11 in which detecting includes directing electromagnetic radiationinto the sample cell and detecting electromagnetic radiation emittedfrom the sample cell.
 13. The method of claim 11 in which detectingferrous and/or conducting particles above said predetermined sizeincludes passing the fluid through a first stage magnetometer sensorsubsystem with a small diameter fluid conduit having a small diametersense coil thereabout and detecting ferrous and/or conducting particlesabove and below the predetermined size includes passing the fluidthrough a second stage magnetometer sensor subsystem with a largerdiameter fluid conduit having a larger diameter sense coil thereabout.14. The method of claim 13 in which the larger diameter fluid conduit isupstream or downstream of a small diameter fluid conduit.
 15. The methodof claim 13 in which the filling factor of the small diameter sense coilis optimized for ferrous and/or conducting imagable particles.
 16. Themethod of claim 13 in which the filling factor of the large diametersense coil is optimized for particle sizes above and below saidpredetermined size.
 17. The method claim 13 in which detecting ferrousand/or conducting particles above said predetermined size includesdetecting the amplitude and phase of the voltage of the small diametersense coil.
 18. The method of claim 13 in which detecting ferrousparticles above and below the predetermined size includes detecting theamplitude and phase of the voltage of the larger diameter sense coil.19. The method of claim 13 in which the small diameter conduit isbetween 250 and 750 microns in diameter.
 20. The method of claim 13 inwhich the larger diameter conduit is between 1,500 and 15,000 microns indiameter.
 21. A particle counting and classification method comprising:imaging a sample to determine the size and morphology of particles abovea predetermined size in a fluid in a sample cell; detecting anddetermining the size of ferrous and/or conducting particles in saidfluid above said predetermined size; and calculating and reporting thenumber of particles in the fluid in a plurality of size ranges, theirmorphology, their classification as a particular particle type accordingto their characteristic morphology and the number of ferrous and/orconducting particles in said size ranges, including: initiallyclassifying said particles in different size ranges based on imaging andadjusting said initial classification based on the detected anddetermined size of ferrous and/or conducting particles in said fluidabove said predetermined size.
 22. The system of claim 1 in which saidindividual particles are classified by morphology.
 23. The system ofclaim 22 in which said morphology classification is cutting wear,sliding wear, fatigue wear, fibers, water droplets, or air bubbles. 24.The system of claim 1 in which said feedback information from said firststage magnetometer sensor subsystem includes identification of saidindividual particles as ferrous and/or conducting particles.
 25. Thesystem of claim 1 in which the overall ferrous content is validated bycomparing information received from the first stage magnetometer sensorsubsystem with information received from the second stage magnetometersensor subsystem.